TARC material for immersion watermark reduction

ABSTRACT

A coating material disposed overlying a photo sensitive layer during an immersion lithography process includes a polymer that is substantially insoluble to an immersion fluid and an acid capable of neutralizing a base quencher from the photo sensitive layer.

CROSS REFERENCES

The present application claims the benefit of U.S. Ser. No. 60/722,316and U.S. Ser. No. 60/722,646, both of which were filed Sep. 30, 2005,and both of which are hereby incorporated by reference.

BACKGROUND

As semiconductor fabrication technologies are continually progressing tosmaller feature sizes such as 65 nanometers, 45 nanometers, and below,immersion lithography processes are being adopted. However, immersionlithography processes induce water drop residue after an exposureprocess. Such water drop residue can cause water mark defects andtherefore degrade or even cause failures during semiconductorfabrication.

What is needed is an improved material for the substrate being exposed,such as a top anti-reflection coating (TARC), wherein the damage causedby water mark defects are prevented and/or reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a sectional view of an exemplary semiconductor device100 having a coating material layer for use during an immersionlithography exposing process.

FIG. 2 illustrates a schematic view of an exemplary reaction between aquencher and a chelate compound.

FIG. 3 is a flowchart of one embodiment of a method of immersionphotolithography patterning.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of variousembodiments. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed interposing thefirst and second features, such that the first and second features maynot be in direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the purpose of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed.

FIG. 1 illustrates a sectional view of a semiconductor device 100, suchas a semiconductor wafer. The semiconductor device 100 includes asubstrate 110 having an organic bottom anti reflecting coating (BARC),an inorganic bottom anti reflective layer, an etch resistance organiclayer, an adhesion enhancement organic layer, various doped regions,dielectric features, and/or multilevel interconnects. In the presentembodiment, the substrate includes silicon, but other embodiments mayinclude Ge, SiGe, GaAs, and so forth. The substrate may alternativelyinclude a non-semiconductor material such as a glass plate forthin-film-transistor liquid crystal display (TFT-LCD) devices. Thesemiconductor device 100 may further include one or more material layersto be patterned.

The semiconductor device 100 includes a photo sensitive layer(photoresist or resist) 120. In the present example, the resist layer120 may have a thickness ranging between about 50 angstroms and 5000angstroms. In another example, the resist layer 120 may have a thicknessranging between about 500 angstroms and 2000 angstroms. The resist layer120 utilizes a chemical amplification (CA) resist material. The resistlayer 120 includes a polymer material that turns soluble to a developer,such as a base solution, when the polymer is reacted with acid. Theresist 120 further includes a solvent filling inside the polymer. Thesolvent may be partially evaporated off during a baking process. Theresist 120 also includes a photo-acid generator (PAG) 122 material. ThePAG molecules are distributed inside the solvent and polymer. Whenabsorbing photo energy, the PAG 122 decomposes and forms a small amountof acid. The PAG 122 may have a concentration ranging between about 1%and 15% wt of the resist polymer 120.

In the present embodiment, the resist 120 also includes a quenchermaterial 124 that distributes inside the solvent and polymer. Thequencher 124 is a base type and is capable of substantially neutralizingacid. Collectively or alternatively, the quencher may inhibit otheractive component of the resist 120 such as inhibiting PAG from reaction.The quencher 124 may have a concentration larger than about 1% wt of theresist polymer. The quencher 124 may alternatively have a concentrationabout one fourth of the concentration of the PAG 122 by weight beforethe exposing process. In one example, each molecule of the quencher 124includes a nitrogen atom having an unpaired electron that is capable ofneutralizing an acid. The resist layer 120 may be formed on thesubstrate 110 by a method such as spin-on coating. Other processinvolved may include a soft baking after the coating process.

In the present embodiment, a coating material layer 130 overlies theresist layer 120. The coating material 130 includes a polymer 132 thatis substantially insoluble to an immersion fluid. In one example, thepolymer 132 contains fluoride. The coating material 130 includes an acid134. The coating material 130 may have a pH value below about 5. Theacid 134 may be chemically bonded to the polymer 132. The chemicallybonded acid 134 and the polymer 132 may form a copolymer that has anorganic acid functional group. The organic acid functional group mayinclude a carboxylic group, hydroxyl group, a thiol group, an enolgroup, a phenol group, a sulfonyl acid group, a SO₂OH group, orcombinations thereof. The acid 134 may be alternatively distributed inthe coating material layer 130 mixed to the polymer. The acid for thispurpose may include surfactant, additive, buffer, and other suitablechemicals. The acid additives may include organic acid or inorganicacid. The organic acid may be selected from the group consisting of acarboxylic group, hydroxyl group, a thiol group, an enol group, a phenolgroup, a sulfonyl acid group, a SO₂OH group, and combinations thereof.The inorganic acid may be selected from the group consisting ofperchloric acid, hydrogen iodide, hydrogen bromide, hydrogen chloride,nitric acid, thiocyanic acid, chloric acid, iodic acid, hypophosphorousacid, hydrogen fluoride, nitrous acid, cyanic acid, hydrazoic acid,hypochlorous acid, hypobromous acid, hydrocyanic acid, hypoiodous acid,sulfuric acid, chromic acid, sulfurous acid, phosphoric acid,phosphorous acid, pyrophosphoric acid, carbonic acid, hydrogen sulfide,boric acid, and combinations thereof. In another example, the organicacid may include a PAG in the coating material layer, bonded or notbonded to the polymer 132. The PAG in the coating material 130 may betransformed into an acid at an exposing process such as an exposingprocess for resist patterning. The coating material layer 130 mayfurther include solvent in the polymer. The solvent may includeperfluoro solvent such as hydrofluroether C₄F₉OCH₃. The solvent mayalternatively include PGME/PGMEA mixture solvent. The mixture ratio mayrange between about 10/1 to 1/10. For example, the mixture ratio isabout 7/3 in one example. The solvent may include alcohol solvent, suchas cyclohexanol, butanol, iso-butanol, pentanol, or iso-pentanol. Thesolvent may alternatively include water-based solvent.

Alternatively, the coating material 130 may include a chelate compoundinstead of an acid. The chelate compound is capable to react with thequencher and chemically bond therewith. The reaction between the chelatecompound and the quencher may lead to a larger molecule, a reducedmobility of the quencher, and/or may inactivate the quencher byneutralizing the nitrogen of the quencher, for example. The chelatecompound may be chemically bonded to the polymer. Thus the reactionbetween the quencher and the chelate compound can lead to that thequencher is bonded to the polymer.

FIG. 2 illustrates a schematic view of an example of a reaction betweena quencher and a chelate compound. A quencher 202 having a tertiaryamine may react with a chelate compound 204 having a halogenalkane andforms a quaternary ammonium salt 206.

Referring again to FIG. 1, the coating layer may be integral to a topanti-reflective coating layer (TARC) with an enhanced reflection to aradiation energy during an exposing process. The coating material layer130 may be alternatively formed above or below a separate TARC layer.The coating material layer 130 may include a multiple layer structure(composite layer). For example, the coating material layer 130 mayinclude a dual layer structure having a first coating layer and a secondcoating layer disposed on the first coating layer. The first and secondcoating layers may include different materials tuned for intendedfunctions. The first coating layer may be disposed on top of the resistlayer 120 and may be designed to function as a quencher catch layer toneutralize the quencher diffused from the resist layer 120. To avoidresist intermixing during the coating, the solvent of the first coatinglayer may be different from that of the resist layer. For example, ifthe resist layer is a PGME/PGMEA solvent, the first coating layer mayutilize an alcohol solvent. The second coating layer may be a polymernetwork cross-linked at a baking process, or may utilize a normalsolvent such as PGME/PGMEA solvent to eliminate intermixing.Alternatively, the first coating layer may be cross-linked and thesecond coating layer may utilize a normal solvent such as a PGME/PGMEAsolvent. The second coating layer may be designed to isolate the resistlayer from the immersion fluid, eliminating fluid uptake from theimmersion fluid such as de-ionized water (DIW). Collectively oralternatively, the second coating layer may be designed to preventresist composition leaching from the resist layer 120. The function ofthe first and second coating layers may be switched to make the fistlayer as an isolation and second layer as a quencher neutralizer.

The coating material layer 130 may be substantially soluble in a basesolution, a developing solution, or a solvent. An example of the basesolution may include a tetramethylammonium hydroxide (TMAH) solution. Anexample of the solvent may include cyclohexanol, butanol, iso-butanol,pentanol, or iso-pentanol. The resist layer 120 may include a solutionsuch as PGMEA or PGME. The coating material layer 130 may be spin-oncoated thereon and may be further baked. The baking process is integralto the baking process of the resist layer 120 or independent from resistlayer baking.

During an exposing process, the resist layer 120 and the coatingmaterial layer 130 are exposed to a radiation energy such as deepultra-violet (DUV) through a photomask (mask or reticle) having apredefined pattern and an immersion fluid, resulting a resist patternhaving a plurality of unexposed regions such as unexposed features 120 aand a plurality of exposed regions such as exposed features 120 b. Theradiation energy may include 248 nm beam by Krypton Fluoride (KrF)excimer lasers or 193 nm beam by Argon Fluoride (ArF) excimer lasers.The immersion fluid may include de-ionized water (DI water or DIW). Theimmersion fluid may further include chemical additives such as an acid.The immersion fluid may alternatively include other suitable fluidhaving an index of refraction higher than 1.44, the index of refractionof water. During an exposing process, water drop residue, such as anexemplary water drop 140, may be left on the coating material layerafter the exposing process.

In previous immersion lithography patterning processes, the water dropresidue may cause problems such as forming a watermark. When a waterdrop is left on a resist layer, the water drop provides a path to PAGand quencher. The quencher in the unexposed resist region may diffusedinto the water drop and further diffuse into the exposed resist region,neutralize photo generated acid, and reduce exposing efficiency in theseexposed areas. Furthermore, the exposed PAG is decomposed as PAG anionand acid, which is more soluble to water than unexposed PAG. The photogenerated acid may also diffuse into the water drop with additionaleffect such that these exposed areas may have reduced photo generatedacid. These exposed areas of the resist layer thus may have insufficientphoto generated acid to induce a cascade of chemical transformations(acid amplification) after the exposing process step, and may not befully soluble in developing solution at a developing process step. Thusan unexpected T-top resist feature (watermark) may be formed on theexposed regions of the resist layer in which the top resist material ofthe exposed region are not soluble in a developing solution.

According to the present disclosure, the coating material layer isolatesthe water drops from the resist layer 120. When the quencher 124 isdiffused into the coating material layer 130, it will be reacted witheither the acid of the coating material 130 or a chelate compound suchthat the diffused quencher is neutralized, trapped, or transformed intoa molecule with a reduced mobility and/or no quenching function. Thefurther diffusion of the quencher into the water drops is thus reducedor eliminated. The coating material layer 130 with acid may furtherreduce photo generated acid diffusing out from the resist layer 120. Asan example, the acid leached into the water drops may be less than about10⁻⁹ mole/cm² during an immersion lithography.

In various embodiments, the diffusion of the quencher to water drops issubstantially reduced and the watermark is substantially reducedaccordingly. Various embodiments may be modified or combined foroptimized resist patterning process.

Referring to FIG. 3, a flowchart of an immersion lithography method 300to form a resist pattern is described. The method 300 includes a step302 to form a photo sensitive (resist) layer on a semiconductor water.The resist layer is substantially similar to the resist layer 120 ofFIG. 1.

The method 300 further include a step 304 to form a coating materiallayer on the resist layer wherein the coating material layer may besubstantially similar to the coating material layer 130 of FIG. 1. Thecoating material layer may include an acid or a chelate compoundfunctioning as quencher catcher. The acid or chelate compound may bechemically bonded to the polymer of the coating material.

The method 300 further includes a step 306 to expose the resist layer toa radiation energy such as DUV through a photomask and an immersionfluid. The immersion fluid may be DIW or other suitable fluid having ahigh index of refraction, and is disposed between the semiconductorwafer and lens of an immersion lithography system to implement themethod 300. Since the coating material layer is formed on the resistlayer, the quencher has a reduced amount of leaching to water drops lefton or over the coating material layer after the exposing step.

The method 300 then proceeds to a step 308 to bake (post exposure bakeor PEB) the resist layer. The baking temperature may range between about80° C. and 150° C. The baking may have a duration ranging from about 1to 20 minutes in one example. The baking step may further serve toremove water drops.

The method 300 then proceeds to a step 310 to develop the resist layerin a developing solution. The exposed resist regions are substantiallydissolved. The step 310 may further include a removal step to remove thecoating material layer, separately from or combined with the developingprocess. For example, the coating material layer may be removed in thedeveloping solution with the exposed resist material. The material andmethod are described using a positive resist as example and can beextended to a negative resist.

Thus in one embodiment, the present disclosure provides a coatingmaterial disposed over a photo sensitive layer, for use during animmersion lithography process. The coating material includes a polymerthat is substantially insoluble to an immersion fluid; and an acidcapable of neutralizing a base quencher from the photo sensitive layer.

In some embodiments, the coating material has a pH value below about 5.The acid may be chemically bonded to the polymer. The acid may beselected from a group consisting of an acid buffer chemical and an acidchemical. The acid may include an organic acid and/or an inorganic acid.The organic acid may include an organic acid functional group attachedto one of an alkyl group and an aromatic group of the polymer. Theorganic acid may include a photo acid generator (PAG). The organic acidmay include an organic acid functional group such as a carboxylic group,hydroxyl group, a thiol group, an enol group, a phenol group, a sulfonylacid group, and/or a SO₂OH group. The inorganic acid may includeperchloric acid, hydrogen iodide, hydrogen bromide, hydrogen chloride,nitric acid, thiocyanic acid, chloric acid, iodic acid, hypophosphorousacid, hydrogen fluoride, nitrous acid, cyanic acid, hydrazoic acid,hypochlorous acid, hypobromous acid, hydrocyanic acid, hypoiodous acid,sulfuric acid, chromic acid, sulfurous acid, phosphoric acid,phosphorous acid, pyrophosphoric acid, carbonic acid, hydrogen sulfide,and/or boric acid. The polymer and acid structure may include fluoride.The coating material may be substantially soluble by a solution selectedfrom the group consisting of a developing solution, a base solution, anda solvent. The base solution may include tetramethylammonium hydroxide(TMAH) solution. The solvent may include cyclohexanol, iso-butanol, oriso-pentanol. The coating material may include a multiple layerstructure.

In another embodiment, a coating material is disposed over a photosensitive layer having a quencher capable of neutralizing acid during animmersion lithography process. The coating material includes a polymerthat is substantially insoluble to an immersion fluid and either an acidcapable of neutralizing the quencher from the photo sensitive layer, ora chelate compound capable of bonding the quencher from the photosensitive layer, or both. The coating material may be designed tofunction as a top anti-reflective coating (TARC) layer. The chelatecompound may be bonded to the polymer. The chelate compound may includea halogenalkane. The chelate compound may be capable of reacting withthe quencher to form quaternary ammonium salts.

An embodiment of a method for immersion photolithography process is alsodisclosed. The method includes forming a photoresist layer on asubstrate, the photoresist layer including a quencher capable ofneutralizing acid. A coating material layer is formed over thephotoresist layer, wherein the coating material layer includes: an acidcapable of neutralizing the quencher from the photo sensitive layer anda polymer that is substantially a carrier of the acid and issubstantially insoluble to an immersion fluid. The method furtherincludes exposing the photoresist layer through a patterned photomaskand the immersion fluid using an immersion lens system. The immersionlens system may include a numerical aperture greater than about 0.85.The photoresist layer is baked and developed.

The foregoing has outlined features of several embodiments so that thoseskilled in the art may better understand the detailed description thatfollows. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A coating material disposed over a photosensitive layer and for useduring an immersion lithography process, the coating materialcomprising: an acid that substantially neutralizes a base quencherdiffusing into the coating material from the photosensitive layer; and apolymer that is substantially a carrier of the acid and is substantiallyinsoluble to an immersion fluid used in the immersion lithographyprocess.
 2. The coating material of claim 1, wherein the acid ischemically bonded to the polymer.
 3. The coating material of claim 1,wherein the acid comprises an organic acid.
 4. The coating material ofclaim 3, wherein the organic acid comprises a sulfonyl acid group. 5.The coating material of claim 1, wherein the acid is mixed to thepolymer.
 6. The coating material of claim 1, wherein the polymercomprises fluoride.
 7. The coating material of claim 1, wherein thecoating material is substantially soluble in a base solution.
 8. Thecoating material of claim 7, wherein the base solution comprisestetramethylammonium hydroxide (TMAH) solution.
 9. The coating materialof claim 1, wherein the coating material is substantially soluble in asolvent.
 10. The coating material of claim 9, wherein the solventcomprises cyclohexanol.
 11. A coating material disposed over aphotosensitive layer and for use during an immersion lithographyprocess, the coating material comprising: a chelate compound that bondsa quencher diffusing into the coating material from the photosensitivelayer; a polymer that is substantially insoluble to an immersion fluidused in the immersion lithography process.
 12. The coating material ofclaim 11, wherein the chelate compound is chemically bonded to thepolymer.
 13. The coating material of claim 11, wherein the chelatecompound comprises a halogenalkane.